Magnetic disk apparatus and method of detecting head fault

Abstract

According to the present invention, there is provided a magnetic disk apparatus comprising a reading/writing circuit for detecting first to fourth burst signals corresponding to first to fourth burst data items recorded on a recording medium in order to position a head, a CPU for calculating a first value expressed by ((first burst signal)-(second burst signal))/((first burst signal)+(second burst signal)) and a second value expressed by ((third burst signal)-(fourth burst signal))/((third burst signal)+(fourth burst signal)) from the amplitudes of the first to fourth burst signals detected by the reading/writing circuit to move the head to a position at which the obtained first value and the obtained second value coincide with each other, a ROM for storing a reference value with which abnormality of the head is determined and a CPU for determining whether or not the difference between the absolute value of the first value when the head has been moved to the position at which the first value and the second value coincide with each other and the reference value stored in the ROM is larger than a predetermined value to detect abnormality of the head in a case where a determination has been performed that the difference between the absolute value of the first value and the reference value is larger than the predetermined value.

I claim: 
     
       1. A magnetic disk apparatus comprising: detection means for detecting first to fourth burst signals corresponding to first to fourth burst data items recorded on a recording medium in order to position a head;   calculating means for calculating a first value expressed by ((the first burst signal)-(the second burst signal))/((the first burst signal)+(the second burst signal)) and a second value expressed by ((the third burst signal)-(the fourth burst signal))/((the third burst signal)+(the fourth burst signal)) from amplitudes of the first to fourth burst signals detected by said detection means;   control means for moving said head to a position at which the first value and the second value obtained by said calculating means coincide with each other;   storage means for storing a reference value with which abnormality of said head is determined;   first determination means for determining whether or not difference between an absolute value of the first value and the reference value stored in said storage means when said head has been moved to the position at which the first value and the second value coincide with each other by said control means is larger than a predetermined value; and   abnormality detection means for detecting abnormality of said head in a case where said first determination means has determined that a difference value between the absolute value of the first value and the reference value is larger than the predetermined value.   
     
     
       2. The magnetic disk apparatus according to claim 1, wherein said control means performs head moving process and said abnormality detection means performs abnormality detection process during an initialization process which is performed after electric power has been supplied to said magnetic disk apparatus.   
     
     
       3. The magnetic disk apparatus according to claim 1, wherein the reference value is stored in said storage means when said magnetic disk apparatus is manufactured.   
     
     
       4. The magnetic disk apparatus according to claim 1, wherein said storage means is an EEPROM.   
     
     
       5. The magnetic disk apparatus according to claim 1, wherein the reference value is the first value when said head has been moved by said control means to a position at which the first value and the second value coincide with each other when said magnetic disk apparatus has been manufactured.   
     
     
       6. The magnetic disk apparatus according to claim 1, wherein said abnormality detection means comprises:   dummy writing means for performing a dummy writing operation in a case where said first determination means has determined that the absolute value of the first value is larger than the reference value;   second determination means for determining whether or not said dummy writing means has performed the dummy writing operations by a predetermined number of times; and   means for detecting abnormality of said head in a case where said second determination means has determined that the dummy writing operations have been performed by the predetermined number of times.   
     
     
       7. A magnetic disk apparatus structured to detect burst signals i and j corresponding to burst data i and j from a recording medium on which at least three burst data pairs each having burst data i and j have been recorded, to position a head thereof in accordance with detected burst signals i and j, said magnetic disk apparatus comprising: calculating means for obtaining a result of a calculation expressed by (i-j)/(i+j) for each pair from amplitudes of the burst signals i and j in two arbitrary pairs among the detected burst signals i and j;   control means for moving said head to a position at which results of calculations of the two arbitrary pairs obtained by said calculating means coincide with each other;   storage means for storing a reference value for determining abnormality of said head;   first determination means for determining whether or not difference between an absolute value of the result of the calculation when said head has been moved to the position at which the results of calculations of the two arbitrary pairs coincide with each other by said control means and the reference value stored in said storage means is larger than a predetermined value; and   abnormality detection means for detecting abnormality of said head in a case where said first determination means has determined that the difference between the absolute value of the result of the calculation and the reference value is larger than the predetermined value.   
     
     
       8. The magnetic disk apparatus according to claim 7, wherein said control means performs head moving process and said abnormality detection means performs abnormality detection process during an initialization process which is performed after electric power has been supplied to said magnetic disk apparatus.   
     
     
       9. The magnetic disk apparatus according to claim 7, wherein the reference value is stored in said storage means when said magnetic disk apparatus is manufactured.   
     
     
       10. The magnetic disk apparatus according to claim 7, wherein said storage means is an EEPROM.   
     
     
       11. The magnetic disk apparatus according to claim 7, wherein the reference value is a result of a calculation when said head has been, by said control means, moved to the position at which the results of the calculations of the two arbitrary pairs coincide with each other when said magnetic disk apparatus has been manufactured.   
     
     
       12. The magnetic disk apparatus according to claim 7, wherein said abnormality detection means comprises:   dummy writing means for performing a dummy writing operation in a case where said first determination means has determined that the absolute value of the first value is larger than the reference value;   second determination means for determining whether or not said dummy writing means has performed the dummy writing operations by a predetermined number of times; and   means for detecting abnormality of said head in a case where said second determination means has determined that the dummy writing operations have been performed by the predetermined number of times.   
     
     
       13. A method of detecting a fault of a head, comprising the steps of: detecting first to fourth burst signals corresponding to first to fourth burst data items recorded on a recording medium in order to position a head;   calculating a first value expressed by ((the first burst signal)-(the second burst signal))/((the first burst signal)+(the second burst signal))     and a second value expressed by ((the third burst signal)-(the fourth burst signal))/((the third burst signal)+(the fourth burst signal)) from amplitudes of detected first to fourth burst signals;     moving said head to a position at which the first value and the second value coincide with each other;   determining whether or not the difference between an absolute value of the first value and the reference value when said head has been moved to the position at which the first value and the second value coincide with each other is larger than a predetermined value; and   detecting abnormality of said head in a case where a determination has been performed that the difference between the absolute value of the first value and the reference value is larger than the predetermined value.   
     
     
       14. The method of detecting a fault of a head according to claim 13, wherein the head moving process and the abnormality detection process are performed during an initialization process which is performed after electric power has been supplied to the magnetic disk apparatus.   
     
     
       15. The method of detecting a fault of a head according to claim 13, wherein the reference value is the first value when said head has been moved to the position at which the first value and the second value coincide with each other when said magnetic disk apparatus has been manufactured.   
     
     
       16. The method of detecting a fault of a head according to claim 13, wherein the step of detecting abnormality comprising the steps of: performing a dummy writing operation in a case where a determination has been performed that the absolute value of the first value is larger than the reference value;   determining whether or not the dummy writing operations have been performed by a predetermined number of times; and   detecting abnormality of said head in a case where a determination has been performed that the dummy writing operations have been performed by the predetermined number of times.     
     
     
       17. A method of detecting a fault of a head comprising the steps of: detecting burst signals i and j corresponding to burst data i and j from a recording medium on which at least three burst data pairs each having burst data i and j have been recorded;   obtaining a result of a calculation expressed by (i-j)/(i+j) for each pair from amplitudes of the burst signals i and j in two arbitrary pairs among the detected burst signals i and j;   moving said head to a position at which results of calculations of two arbitrary pairs coincide with each other;   determining whether or not difference between an absolute value of the result of the calculation when said head has been moved to the position at which the results of calculations of the two arbitrary pairs coincide with each other and a reference value is larger than a predetermined value; and   detecting abnormality of said head in a case where a determination has been performed that the difference between the absolute value of the result of the calculation and the reference value is larger than the predetermined value.   
     
     
       18. The method of detecting a fault of a head according to claim 17, wherein the head moving process and the abnormality detection process are performed during an initialization process which is performed after electric power has been supplied to said magnetic disk apparatus.   
     
     
       19. The method of detecting a fault of a head according to claim 17, wherein the reference value is the result of the calculation when said head has been moved to the position at which the results of calculations of the two arbitrary pairs coincide with each other when said magnetic disk apparatus has been manufactured.   
     
     
       20. The method of detecting a fault of a head according to claim 17, wherein the step of detecting abnormality of said head comprising the steps of:   performing a dummy writing operation in a case where a determination has been performed that the absolute value of the first value is larger than the reference value;   determining whether or not the dummy writing operations have been performed by a predetermined number of times; and   detecting abnormality of said head in a case where a determination has been performed that the dummy writing operations have been performed by the predetermined number of times.